Mold Steel Composition for High-Temperature Strength and Thermal Conductivity
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Solution Overview
Problem
Mold steels used in high-temperature applications face challenges in simultaneously achieving high-temperature strength, corrosion resistance, excellent annealing properties, high productivity, and fine austenite crystal grains during quenching, while also requiring reduced material costs and efficient heat treatment processes.
Innovation Solution
A mold steel composition with specific ranges of C, Si, Mn, Cr, Cu, Ni, Mo, V, and N is formulated to achieve a hardness above 33 HRC and below 57 HRC, with a grain size number of prior austenite at quenching of 5 or more, and thermal conductivity exceeding 27.0 W/m/K, utilizing the pinning and solute drag effects to refine austenite crystal grains and enhance thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high Cr content is added to improve high-temperature strength and corrosion resistance, then these properties are improved, but thermal conductivity decreases and material cost increases
Solution Approach 1:
The patent optimizes the Cr content parameter to a specific range (2.00-3.50 mass%) rather than using high amounts, and combines it with controlled amounts of Mo and V to achieve the required high-temperature strength while limiting the negative impact on thermal conductivity. This parameter optimization resolves the contradiction between strength improvement and thermal conductivity maintenance.
Solution Approach 2:
The patent creates a composite alloy system combining Cr, Mo, and V elements in specific proportions. This multi-element composite approach allows the steel to achieve high-temperature strength through synergistic effects of multiple alloying elements rather than relying solely on high Cr content, thereby preserving thermal conductivity.
2Reliability
If high Cr content is added to improve corrosion resistance, then corrosion resistance is improved, but material cost increases
Solution Approach 1:
The patent sets Cr content within an optimized range (2.00-3.50 mass%) that provides sufficient corrosion resistance for die casting molds while avoiding excessive Cr addition that would unnecessarily increase material cost. This parameter control balances performance requirements with cost considerations.
Solution Approach 2:
The patent employs a composite alloying strategy combining Cr with Mo and V elements. This composite approach distributes the corrosion resistance function across multiple elements, allowing reduced Cr content while maintaining overall corrosion resistance, thereby reducing material cost.
3Strength
If conventional quenching heat treatment is performed to achieve required hardness, then hardness is improved, but austenite crystal grains coarsen and productivity decreases
Solution Approach 1:
The patent incorporates alloying elements (Cr, Mo, V) in specific amounts during steelmaking to pre-establish grain refinement capabilities and hardenability. This preliminary action ensures that subsequent quenching produces fine grains and required hardness without requiring excessively long heating times, thereby improving productivity.
Solution Approach 2:
The patent optimizes the composition parameters (Cr: 2.00-3.50%, Mo: 0.50-3.29%, V: 0.55-1.13%) to achieve a balance between hardenability and grain growth resistance. This parameter optimization allows quenching to be performed at practical heating times (1-3 hours) while still achieving both fine grains and required hardness, resolving the productivity contradiction.
4Productivity
If multiple mold sizes are heated simultaneously to improve productivity, then productivity is improved, but crystal grain coarsening occurs in smaller molds
Solution Approach 1:
The patent incorporates grain-refining alloying elements (particularly V and Mo) in specific amounts during steelmaking to pre-establish grain boundary pinning capability. This preliminary action ensures that during simultaneous heat treatment of multiple mold sizes, the smaller molds maintain fine grains even with extended heating time, enabling productivity improvement without grain coarsening.
Solution Approach 2:
The patent optimizes the V content (0.55-1.13 mass%) and Mo content (0.50-3.29 mass%) to provide strong grain boundary pinning effect. This parameter control allows simultaneous heating of multiple mold sizes at practical temperatures and times while preventing grain coarsening in smaller molds, resolving the contradiction between productivity and grain size control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a mold steel with improved high-temperature strength, corrosion resistance, and annealing properties, enabling fine austenite crystal grains during quenching, reduced cycle times, and cost-effective heat treatment processes, while preventing cracking and maintaining high thermal conductivity.
Implementation Method 1
the contents of C, V and N relating to VC particles, which suppress the movement of a grain boundary by the pinning effect, are adjusted
Implementation Method 2
the contents of Cu, Ni and Mo as solid solution elements, which suppress the movement of a grain boundary by the solute drag effect, are adjusted
Data Source
AI summary
The mold steel according to the present invention contains 0.35<C<0.55 mass %, 0.003≤Si<0.300 mass %, 0.30<Mn<1.50 mass %, 2.00≤Cr<3.50 mass %, 0.003≤Cu<1.200 mass %, 0.003≤Ni<1.380 mass %, 0.50<Mo<3.29 mass %, 0.55<V<1.13 mass %, and 0.0002≤N<0.1200 mass %, with a balance being Fe and unavoidable impurities, and satisfies 0.55<Cu+Ni+Mo<3.29 mass %, and the molding tool according to the present invention contains a mold and/or a mold component formed of the mold steel.